1. Field of Invention
This invention relates to sensing the fluid level in a server as used in a beverage brewing device, and securing servers of various heights in a beverage brewing device, such as a coffee maker.
2. Prior Art
Coffee makers on aircraft are used many times per month and therefore must be very reliable. The current art, U.S. Pat. No. 4,949,627, uses “swingably” mounted electrodes to detect when the coffee maker server is full and to therefore stop filling the server. These electrodes are conductive metal segments linked together by conductive pins, bolts, and nuts. The problem with this design is the fact that over time coffee residue builds up between the links and between the pins and links. This residue reduces the electrical conductivity of the electrode linkage, and thus renders the electrode sensor inoperable and causing the server to overflow. One conventional technique for solving the problem of residue interrupting electrical conductivity in electrodes is to use a probe without links. Instead of “swingably” mounted electrodes, probes mounted with springs are used. This provides an electrode without gaps to become contaminated. These probes are always oriented downward into the server. When the server is put into the coffee maker the probes are pushed out of the way by the server and then flex back into position inside the server. A problem occurs if the server is not pushed fully into position in the coffee maker. The probes of the current art will not spring back inside the server opening and the coffee maker will overfill the server since the probes are outside the server. Another problem with the current art occurs because the spring mounted probes become damaged over time with repeated flexing of the mounting springs and being repeatedly impacted by the server. The current art, U.S. Pat. No. 7,017,408, attempted to eliminate the mechanical failures associated with spring mounted probes by replacing conductive probes with infrared light emitting diodes (IRED) to detect the liquid level in the server. The IRED concept has problems with the lenses becoming dirty from steam and coffee residue which cause the IRED concept to not detect the liquid surface and therefore overfilling the occurs. The IRED also has difficulty detecting the liquid surface when the surface is vibrating due to aircraft vibration. The IRED concept also has errors detecting the maximum allowed surface level when the aircraft is not in level flight since the liquid surface is not horizontal. Problems also occur with the IRED concept in detecting the liquid surface due to the presence of steam. All of these problems cause the IRED concept to overflow the server. Another problem with the current art, U.S. Pat. No. 6,227,101, is the use of a stationary brew tray. The brew tray is in a fixed position and brewed liquid exits the “tray access port” through a “shelf access hole” and then into the coffee pot. This requires the brewed liquid to pour across a gap between the “shelf access hole” and the coffee pot. When the aircraft is not in level flight, the liquid travelling across this gap can miss entering the coffee pot, causing spillage. In order to minimize the gap across which the brewed liquid must pour, the current art requires the container into which the liquid pours to be a specific height. The current art, U.S. Pat. No. 6,227,101, secures the server in the coffee maker with “a pair of spaced apart fingers.” This mechanism can only engage servers of a specific height. This forces the operator to use specific servers with specific height geometry. Also, the current art is difficult to clean due to the use of a fixed brew tray. This requires cleaning of the “tray access port” which is difficult to access.